1. Field of the Invention
The present invention relates generally to the preparation of bone and cartilage transplants for reconstruction of the acetabulum, femoral head, or both, using tissue engineered osteochondral constructs and/or an osteochondral allograft transplant.
2. Discussion of Related Art Including Information Disclosed Under 37 CFR §§1.97, 1.98
The reconstruction of human joints is an area of ongoing investigation. Since the work of Erich Lexer in the early part of the twentieth century, entire joints have been transplanted into human patients. These large grafts, termed “allografts,” were initially associated with high failure rates and cartilage degeneration. Additionally, patients were required to immobilize and avoid bearing weight on the treated joint for long periods.
In the early 1970's, the concept of shell allografts of fresh bone and cartilage was introduced. With these grafts, only a thin shell of bone was transplanted, in essence as a carrying vehicle for the fresh articular cartilage which would remain populated with cells from the donor. Once the bone of the host healed to the graft bone, the articular cartilage would continue to receive its nutrition from the synovial fluid in the joint. The bone, due to its small volume, generated a minimal immune response. Using this technique, large areas of articular cartilage could be repaired with normal cartilage without the need for systemic immunosuppressive medications. The success of this surgical procedure has been documented based on both clinical improvements as well as documented long-term donor cell viability for nearly 30 years after the transplantation.
In the area of instrumentation for fresh osteochondral allografts, current preparation systems are almost universally based on the preparation of cylindrical cores that can be trimmed and transplanted into matched cylindrically prepared recipient sites in the complementary position of the joint. In U.S. Pat. No. 6,488,033, Cerundolo describe obtaining and placing an osteochondral allograft in the same location of the joint and in the same orientation to optimize the surface matching of the graft surface to the native joint. However, this invention does not shed any light or provide any solution to the challenges in performing a total joint allograft on a ball and socket joint such as the hip, nor does this invention discuss any automated jig for achieving precise orientation in the preparation of the grafts. Schmieding presents a method and instrumentation for the preparation, distribution, and insertion of round, size specific osteochondral allografts in U.S. Pat. No. 6,591,581. In this document, the distribution network for fresh osteochondral allografts is laid out, along with details for instrumentation in preparing such osteochondral plugs and recipient sites. This instrumentation is analogous to that discussed in U.S. Pat. No. 5,919,196 for autologous osteochondral transfer, otherwise known as mosaicplasty. However, no insights are offered into the challenges of preparing an osteochondral allograft total hip replacement.
In spite of the success in multiple anatomical areas, the use of fresh osteochondral allografts in the hip joint had been limited by the architectural constraints of this joint and the lack of a technique for preparation of grafts to allow for a uniform thickness and architecture. Up to now, the only treatment for replacement of the entire hip joint has been total joint arthroplasty with metal, ceramic and/or polyethylene implants. There are a number of limitations with these options particularly in the very young patient with hip disease. The longevity of traditional hip replacements has been limited by a phenomenon known as osteolysis, whereby debris, usually from the polyethylene bearing, is deposited along the prosthesis and leads to a cellular cascade leading to digestion of the bone and loss of its mechanical integrity, ultimately leading to loosening with large cavitary defects in the bone. Newer technology has become available over the past ten years including the cross linking of polyethylene, the use of ceramic on ceramic bearings, and the resurgence of metal on metal bearings. Each of these has the potential to decrease long-term debris generated bone lysis and implant loosening. An additional disadvantage of standard hip replacements is the mandatory removal of the entire femoral head and passage of a stem into the medullary canal of the femur. This ultimately leads to decreased loading of the proximal femur and the loss of bone density known as stress-shielding. Recently, there has been a resurgence of interest in a procedure known as total hip resurfacing arthroplasty otherwise known as hip resurfacing. With this technique the femoral head is reshaped but preserved and a metal cap is placed on the head usually using bone cement, in effect recapping the femoral head. The resurgence of hip resurfacing has been made possible with improved metal alloy preparation with improved tolerances between the femoral and acetabular components and improved alloy hardness. With this new technology, metal sockets have become available allowing resurfacing of both sides of the joint to make total hip resurfacing a reality. In spite of the benefits of a head preserving operation, total hip resurfacing is associated with high urine and blood metal ion levels as well as risk of complications such as loosening, avascular necrosis, and femoral neck fracture. Additionally, since metal implants are utilized the joint is placed at risk for future revision arthroplasties. Based on the current state of the art in joint arthroplasty, a need for a biological method for restoration of hyaline articular cartilage in the hip is required.